1. Field of the Invention
The present invention relates to a technique for forming a silver-based conductor film on a surface of an electronic component board including glass.
2. Description of the Related Art
A low temperature co-fired ceramic (LTCC) multilayer printed circuit board is formed by laminating and firing a green sheet of glass ceramic having a sintering temperature of 1000xc2x0 C. or less after conductor paste printing. A bonding pad provided on the surface of the low temperature sintered ceramic multilayer printed circuit board is formed by a thick film processing, for example. More specifically, a thick film conductor paste is printed on the surface of the LTCC multilayer printed circuit board and is then fired. For the thick film conductor paste thus used, Japanese Laid-Open Patent Publication No. 1-298090 has described a conductor composition obtained by kneading silver-based metal powder which can be fired in the air and inorganic additives (such as glass frit, a bismuth compound, zinc and/or a zinc compound, nickel and/or a nickel compound).
For a conductor pattern on the board surface, it is generally required that (1) a solder wettability is good, (2) a bonding strength to the board is great and (3) a bond with a gold wire is reliable.
However, in the case where the conductor pattern on the surface of the LTCC multilayer printed circuit board is formed of a silver-based conductor, it is hard to satisfy all the three requirements (1), (2) and (3) for the conductor pattern. For example, the bonding pad formed of the silver-based conductor is not suitable for the wire bonding of the gold wire.
The present invention has an object to more enhance the reliability of the electrical connection of a silver-based conductor pattern on the surface of a glass ceramic board. In order to achieve the above-mentioned object, according to the present invention, a conductor paste containing silver particles having a specific surface area of 0.3 m2/g to 3.0 m2/g is fired at a temperature having a difference of xc2x150xc2x0 C. from the softening temperature of glass, thereby forming a conductor film on the glass ceramic board.